1Field of the Invention
This invention relates to an ignition distributor for use in a spark ignition type internal combustion engine and, more particularly, to a low-noise ignition distributor capable of suppressing noise due to spark discharge occurring between its rotor and fixed side electrodes.
2. Description of the Prior Art
Noise attendant on spark discharge occurring in the ignition system of an internal combustion engine creates disturbances in broadcasting systems such as televisions and radios and troubles in electronic controlled systems such as an electronic controlled fuel injection system, electronic controlled antiskid system, and electronic controlled automatic transmission system, and the like to endanger safe traffic. Thus, it had been desired to suppress such noise as low as possible.
Such noise is caused mainly by (1) spark discharge occurring between ignition plug electrodes, (2) spark discharge occurring between ignition distributor rotor and fixed side electrodes, and (3) spark discharge occurring between ignition distributor braker contacts. Although several attempts have been made in order to suppress noise resulting from spark discharge enumerated in item (2), they have been found to be insufficient in the following respects:
(A) A rotor electrode with resistive material embedded therein has its noise suppressing effect limited for high frequencies more than 200 MHz due to the presence of distributed capacitance paralleled with the resistor although it can suppress noise by 5 to 6 dB for frequencies less than 200 MHz. Additionally, it causes high ignition energy loss due to the presence of the resistive material of several kiloohms.
(B) A rotor electrode with its surface provided with a high resistive material layer demonstrates high ignition energy loss due to the provision of the high resistive material layer on the electrode surface, low noise suppressing effect of 4 to 5 dB, and a tendency of the high resistive material layer to peel off.
(C) A rotor electrode facing a fixed electrode with an increased gap of 1.524 to 6.35 mm exhibits very high ignition loss due to the increased discharge gap although its noise suppressing effect is as high as 15 to 20 dB. Such very high ignition energy loss is contrary to the recent requirements of positive ignition with high ignition energy for high exhaust emission purifying and high fuel economy.